How to low substrate ph gently?

pH balance what yuo add with acetic acid -- commonly known as vinegar. white distilled vinegar typically can be found around the house. whatever you do, don't over pay for an acid in a bottle tha says "ph down" ... that's silly. usually using citric acid which is nothing special and should not be sold at a premium price. you can get 3 gallons of 5% acetic acid for 3-5 dollars and you use maybe 1-3 mL at at ime.... the pH should balance out over time if you consistently water with a slightly more acidic irrigation over time, then pH-balance to the target pH once the substrate is back where you want it. check callibration on any pH instrument when making any similar decisions... worst thing you can do is think there is a problem then create one while reacting to a figment.

@Organoman thank You, bro, for calming me down. I'm a pretty nervous man when its going about my plants, indeed. But where I can find this peat moss? (I live in central Poland) @Chow_13 I use not soil exactly. It is half soil/half coco+perlite mix. It's soft and fluffy on touch. Also, there's Michor Riza in that substrate and small amount of a bat poo. Prepared all ingredients with ph6.0, but from the beginning of growth (first watering) this mix became ph7.0 and it don't want to drop ph down. I heard Your advice and today will not water them, I will live it for tomorrow. (I have soil moist sensor and now it's on a green mark - middle level of moisture).

Top dressing with a half inch layer of peat moss will help with acidifying the soil slowly and gently. You are pretty well in the good pH range, so I wouldn't stress too much, nothing is perfect in nature and your plant won't really notice if it is 6.5 or 6.9, it will still grow just fine.

It can take several watering's to correct. Just make sure you keep the Water going in correct and you should be fine. Stick with 6.0 until you get where you want to be. Since your in soil watch out how much you water, Let it dry out between watering., Don't want to water log the roots and get rot/ stunted growth. Happy Growing